As more tablets come to market, be prepared to be wowed by the power that some of these slates are capable of. But also be prepared to be disappointed: The tablets already on the market, or coming soon, have a slew of gotchas–especially the lower-cost models you may see advertised at rock-bottom prices.

But if you can’t wait and simply must take the plunge now, keep in mind the following three key points (plus a fourth on a slightly alternative way to go) before you buy.

1. You Get What You Pay For

The rock-bottom-priced tablets you see advertised around the Web carry those low prices for a reason. Typically, they lack the processing power, memory, display quality, or responsiveness (or some combination thereof) to provide a satisfying experience. Not that tablets should be all about specs, but right now, if you’re going to buy, do pay close attention to them. Single-core models, or ones with CPUs less than 1GHz, are going to be slow. Also watch out for resistive touchscreens, which generally lag in responsiveness, and for low-resolution displays.

The one bonus: None of these inexpensive models require a service contract with a carrier, so you’ll have the option to ditch your first tablet with less pain than if you had signed a contract.

2. Service Contracts Risk Your Ability to Upgrade

While it’s possible to get a tablet via a service carrier without a contract, you’ll pay more for that privilege. The unfortunate reality is that many tablets–especially those that have 3G connectivity–are tied to contract obligations with mobile broadband service carriers. That means that if you buy a tablet today with a carrier contract, you’re not going to be eligible for an upgrade anytime soon. Never mind the two-year wait for a contract to expire; in the tablet universe, the technology is evolving so rapidly that the market will shift again in six months, let alone a year or two years.

Nvidia only just got dual-core Tegra 2 products out the door, and already the company has announced its road map for quad-core chips. So before signing up, get a sense that the unit you’re buying is the one you want, and not just a stopgap until the next great thing (though something is always around the corner). The amount you save up front may not offset what you’ll pay down the road–and the freedom to change devices may be something it’s not worth putting a price on.

3. For Android Tablets, Look for Google Services

Let me preface this by saying that a number of alternate app stores are around, including market leader GetJar. But the bottom line is, they’re not the official Google Android Market. Having Android Market on the device–along with other services like maps and e-mail–just makes the experience of using the tablet more fluid, and stronger on the whole. The “Google Experience” enables a certain consistency and expectation of what you’re going to get, so if you’re bothering to plop down the bucks for a tablet now, consider that the more complete and well-rounded your experience, the more likely it is that you’ll love your tablet. Think of what has made Apple’s iPad experience so strong (beyond the easy interface)–it’s the simplicity of accessing a deep array of apps.

4. Consider Snapping Up a First-Gen iPad

Yes, you read that correctly. If your wallet couldn’t handle the original iPad’s prices, iPad 2 will remain out of your reach. But Apple is clearing out its stock of the first-generation iPad–and if that version’s weight and lack of dual cameras or dual-core CPU aren’t dealbreakers for your needs, a first-generation iPad is the most cost-effective way to get a good tablet today. Check out the deals for used iPads, too: Over on eBay, I’ve seen 16GB Wi-Fi models selling for as little as $350.